CN101146083A - OFDM receiver and OFDM signal receiving method - Google Patents

OFDM receiver and OFDM signal receiving method Download PDF

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CN101146083A
CN101146083A CNA2007101546037A CN200710154603A CN101146083A CN 101146083 A CN101146083 A CN 101146083A CN A2007101546037 A CNA2007101546037 A CN A2007101546037A CN 200710154603 A CN200710154603 A CN 200710154603A CN 101146083 A CN101146083 A CN 101146083A
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channel
ofdm
doppler frequency
frequency spectrum
characteristic
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CN101146083B (en
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川内豪纪
服部雅之
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Sony Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
    • H04L25/0232—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals
    • H04L25/0234—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals by non-linear interpolation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0222—Estimation of channel variability, e.g. coherence bandwidth, coherence time, fading frequency
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0212—Channel estimation of impulse response
    • H04L25/0216—Channel estimation of impulse response with estimation of channel length
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/022—Channel estimation of frequency response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/024—Channel estimation channel estimation algorithms
    • H04L25/025—Channel estimation channel estimation algorithms using least-mean-square [LMS] method
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03159—Arrangements for removing intersymbol interference operating in the frequency domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
  • Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)

Abstract

An OFDM receiver may include OFDM-signal receiving means for receiving an orthogonal frequency division multiplexing (OFDM) signal; channel-characteristic estimating means for estimating a channel characteristic using pilot signals in the OFDM signal received by the OFDM-signal receiving means; and transmission-distortion compensating means for applying, on the basis of the channel characteristic estimated by the channel-characteristic estimating means, processing for compensating for transmission distortion to the OFDM signal received by the OFDM-signal receiving means. The channel-characteristic estimating means may include plural kinds of time-direction-channel estimating means used for the estimation of a channel characteristic, and switching control means for switching these estimating means according to a state of a channel.

Description

OFDM receiver and ofdm signal method of reseptance
The cross reference of related application
The present invention is contained in the theme of on September 12nd, 2006 at the Japanese patent application JP 2006-247097 of Japan Patent office submission, and its full content is hereby expressly incorporated by reference.
Technical field
The present invention relates to be used to receive the OFDM receiver and the ofdm signal method of reseptance of OFDM (OFDM) signal and demodulating ofdm signal.
Background technology
The modulating system that is called as OFDM (OFDM) system is used as the modulation and demodulation system of received terrestrial digital broadcasting system.This ofdm system is that the quadrature subcarrier signal that provides transmission band a large amount of is provided, and gives the amplitude and the phase assignments data of each subcarrier signal, and according to PSK (phase shift keying) or QAM (quadrature amplitude modulation) system of modulation signal digitally.
Ofdm system has following characteristic: because transmission band cut apart by a large amount of subcarrier signals, so although the frequency band of each subcarrier signal narrows down and reduced modulating speed, overall emission rate is identical with the emission rate of passing by in the modulating system.Ofdm system also has owing to a large amount of subcarrier signal of parallel transmission, so reduced the characteristic of symbol (symbol) speed.Therefore, in ofdm system, can reduce time span, and launch the less influence that disturbed by multichannel with respect to the multichannel of symbol time length.Further, ofdm system has following characteristic: because with a plurality of subcarriers of the non-dispensing of data, so can transmit and receive circuit by carrying out IFFT (invert fast fourier transformation) computing circuit of inverse fourier transform in use between modulation period and using FFT (fast fourier transform) computing circuit of carrying out Fourier transform to form during demodulation.
Because ofdm system has above-mentioned characteristic, so usually ofdm system is applied to be disturbed by multichannel the received terrestrial digital broadcasting of strong influence.When this ofdm system is used in the ground digital broadcasting, existence such as DVB-T (digital video broadcast-terrestrial), the standard of ISDB-T (ground integrated service digital broadcasting) and ISDB-TSB (integrated service digital broadcasting-ground sound radio) (for example, referring to " Receiver for Terrestrial Digital SoundBroadcast-Standard (Desirable Specifications) ARIB STD-B30 version1.1 ", radio industry and commercial guild, decision on May 31 calendar year 2001, revision on March 28th, 2002, and " Transmission System for Terrestrial Digital SoundBroadcast ARIB STD-B29 version 1.1 ", radio industry and commercial guild, decision on May 31 calendar year 2001, revision on March 28th, 2002).
By transmitting in the symbolic unit transmission OFDM system that is called as the OFDM symbol.This OFDM symbol comprises significant character and protection at interval, and wherein, significant character is the signal period of carrying out IFFT during launching, and in protection at interval, directly duplicates the waveform of this significant character latter half.This protection is set at interval in the first half of OFDM symbol.In ofdm system, this protection is set at interval to improve the multichannel resistance.Concentrate a plurality of OFDM symbols to form an OFDM transmission frame.For example, in the ISDB-T standard, form 10 OFDM transmission frames by 204 OFDM symbols.Set the insertion position of pilot signal as benchmark with this OFDM transmission frame unit.
Be used as in the ofdm system of modulating system of each subcarrier in the modulation of QAM system, because the influence of multichannel etc. between transmission period, amplitude is different with phase characteristic for each subcarrier signal.Therefore, at receiver side, need balanced received signal so that equal for the amplitude and the phase place of each subcarrier.In ofdm system,, in the transmission symbol of transmission signals, insert the pilot signal of predetermined amplitude and predetermined phase discretely in emitting side.At receiver side, use the amplitude of pilot signal and the frequency characteristic of phase calculation channel, and according to the balanced received signal of the characteristic of channel of calculating.
The pilot signal that is used for the calculating channel characteristic is known as scattered pilot (SP) signal.
Summary of the invention
As in the OFDM receiver estimated time direction channel method, use the method for mean type estimator direction estimated time channel, the method for using interpolation type estimator direction estimated time channel and the method for using forecasting type estimator direction estimated time channel as everyone knows.All methods all have merits and demerits on its characteristic.The forecasting type estimator can be periodic channel estimating channel for not free static channel and the time fluctuation that fluctuates exactly.Yet, the forecasting type estimator in the prediction a little less than, and may not be for correctly estimating channel as the channel of the known random fluctuation of typical urban.On the other hand, interpolation type estimator is more remarkable than forecasting type estimator, interpolation type estimator even can estimate there is not the very channel of mistake in the channel of random fluctuation.Yet, when it attempts to obtain to be equal to the performance of forecasting type estimator, need a large amount of taps in the channel of static channel or cyclic fluctuation, therefore, also need to preserve memory of data.When the fluctuation in the channel is when relaxing very much, the mean type estimator obtains preferable performance, but when fluctuation greatly the time, the mean type estimator may not be followed fluctuation.
Therefore, OFDM receiver and ofdm signal method of reseptance need be provided, no matter whether channel is whether the time fluctuation in static, the channel is whether time fluctuation in periodic or the channel is at random, can receive ofdm signal under the situation that does not significantly increase circuit scale.
From then on other purpose that obtains and certain benefits will become more apparent in the following explanation of embodiment.
According to embodiments of the invention, in order under the situation that does not significantly increase circuit scale, to obtain high-performance, no matter and whether the channel time fluctuation whether whether be time fluctuation in static, the channel be in periodic or the channel is at random, switches and use mean type estimator, interpolation type estimator, forecasting type estimator.
According to one embodiment of present invention, provide a kind of OFDM receiver, having comprised: the ofdm signal receiving system is used to receive OFDM (OFDM) signal; The channel characteristic estimation device is used for using the pilot signal of the ofdm signal that is received by the ofdm signal receiving system to estimate the characteristic of channel; And the transmission distortion compensation arrangement, be used for based on the ofdm signal that is received by the ofdm signal receiving system being applied the processing that is used to compensate transmission distortion by channel characteristic estimation device estimated channel characteristic.The channel characteristic estimation device comprises: polytype time orientation channel estimating apparatus is used for the estimation of the characteristic of channel; And switching control, be used for switching these estimation units according to channel status.
According to another embodiment of the invention, provide a kind of ofdm signal method of reseptance: receive OFDM (OFDM) signal; Use the pilot signal in the ofdm signal that is received to estimate the characteristic of channel; And the ofdm signal that is received being applied the processing that is used to compensate transmission distortion based on the estimated channel characteristic, this ofdm signal method of reseptance comprises: the Doppler frequency spectrum of estimating the ofdm signal that received; And, switch the polytype time orientation channel estimating apparatus that is used to estimate the characteristic of channel according to the Doppler frequency spectrum of estimating.
According to embodiments of the invention, when channel be static or channel in time fluctuation when being periodic, use the forecasting type estimator.When the time fluctuation in the channel be at random the time, the forecasting type estimator can be switched to interpolation type estimator and come direction channel estimated time.In other words, can select suitable method of estimation and in all channels, obtain remarkable receptivity according to the state of channel.
Description of drawings
Fig. 1 is the structured flowchart that illustrates according to the OFDM receiver of the embodiment of the invention;
Fig. 2 is the diagrammatic sketch that is used to explain the transmission symbol of ofdm signal;
Fig. 3 is the diagrammatic sketch that is used for explaining the SP signal configures pattern of ofdm signal;
Fig. 4 is the structured flowchart that the pilot tone use channel estimator in the OFDM receiver is shown;
Fig. 5 A and Fig. 5 B are used for explaining the diagrammatic sketch that uses the mean type method of channel estimator direction estimated time channel in pilot tone;
Fig. 6 A and Fig. 6 B are used for explaining the diagrammatic sketch that uses the interpolation type method of channel estimator direction estimated time channel in pilot tone;
Fig. 7 A to Fig. 7 C is the diagrammatic sketch that schematically shows the Doppler frequency spectrum example;
Fig. 8 is used for explaining in pilot tone using channel estimator to pass through the diagrammatic sketch of the subcarrier signal of direction channel estimating estimated time;
Fig. 9 is used for explaining at the diagrammatic sketch of OFDM receiver by the subcarrier signal of frequency direction channel estimator estimation;
Figure 10 is the block diagram that another structure example of the pilot tone use channel estimator in the OFDM receiver is shown;
Figure 11 A and Figure 11 B are used for explaining the diagrammatic sketch that uses the forecasting type method of channel estimator direction estimated time channel in pilot tone;
Figure 12 is the block diagram that the another structure example of the pilot tone use channel estimator in the OFDM receiver is shown;
Figure 13 illustrates the block diagram that pilot tone is used the structure example of the fluctuation type decision device in the channel estimator;
Figure 14 is the flow chart that the decision maker operation in the fluctuation type decision device is shown;
Figure 15 A to Figure 15 C is the diagrammatic sketch that is illustrated schematically in the decision state of the Doppler frequency spectrum shape when not fluctuating;
Figure 16 A to Figure 16 C is the diagrammatic sketch of the decision state of the Doppler frequency spectrum shape when being illustrated schematically in fluctuation for periodicity; And
Figure 17 A to Figure 17 C is illustrated schematically in the diagrammatic sketch that fluctuation is the decision state of the Doppler frequency spectrum shape at random the time.
Embodiment
Below, explain embodiments of the invention with reference to the accompanying drawings in detail.Much less, the embodiment that the present invention is not limited to describe below, and under the condition that does not deviate from spirit of the present invention, can make amendment arbitrarily.
For example, apply the present invention to have the OFDM receiver 10 of structure shown in Figure 1.
OFDM receiver 10 comprises antenna 11, tuner 12, band pass filter (BPF) 13, A/D converter 14, digital orthogonal demodulator 15, FFT computing circuit 16, pilot tone use channel estimator 17, channel distortion compensator 18, error correction circuit 19, transmission parameter decoder 20, postpones section (profile) estimator 21 and window (window) regenerator 22.
The broadcast wave of the digital broadcasting that transmits from the broadcasting station is received by the antenna 11 of OFDM receiver 10 and offers tuner 12 as the RF signal.
Tuner 12 comprises mlultiplying circuit 121 and local oscillator 122.Tuner 12 will be converted to the IF signal by the RF signal frequency that antenna 11 receives.The IF signal that is obtained by tuner 12 carries out filtering by band pass filter (BPF) 13, then by A/D converter 14 digitlizations and offer digital orthogonal demodulator 15.
The IF signal that digital orthogonal demodulator 15 uses the carrier signal quadrature demodulation of preset frequency (carrier frequency) to be digitized, and the ofdm signal of output base band.From the baseband OFDM signal of digital orthogonal demodulator 15 output is to stand the signal so-called time domain before the FFT computing.Therefore, after the digital quadrature demodulation and the baseband signal before the FFT computing be known as the OFDM time-domain signal hereinafter.As the result of quadrature demodulation, this OFDM time-domain signal becomes the complex signal that comprises real axis component (I channel signal) and imaginary axis component (Q channel signal).To offer FFT computing circuit 16, window regenerator 22 by the OFDM time-domain signal of digital orthogonal demodulator 15 outputs and postpone section estimator 21.
16 pairs of OFDM time-domain signals of FFT computing circuit apply the FFT computing, are extracted in the data of quadrature modulation in each subcarrier, and export this data.The signal of output is to stand the FFT computing signal in so-called frequency domain afterwards from FFT computing circuit 16.Therefore, the signal after the FFT computing is known as the OFDM frequency-region signal.
FFT computing circuit 16 extracts the signal in the significant character length range from an OFDM symbol, that is, get rid of protection scope at interval from an OFDM symbol, and the OFDM time-domain signal that extracts is applied the FFT computing.Particularly, as shown in Figure 2, the position of beginning arithmetic operation is that border (the A position Fig. 2) from the OFDM symbol is to the optional position of the terminal position (the B position among Fig. 2) at protection interval.This arithmetic operation scope is known as the FFT window.
By transmitting in the symbolic unit transmission OFDM system that is called the OFDM symbol.This OFDM symbol comprises significant character and protection at interval, and wherein, significant character is the signal period of carrying out IFFT during launching, and in protection at interval, directly duplicates the waveform of this significant character latter half.This protection is set at interval in the first half of OFDM symbol.In ofdm system, this protection is set at interval to improve the multichannel resistance.Concentrate a plurality of OFDM symbols to form an OFDM transmission frame.For example, in the ISDB-T standard, form 10 OFDM transmission frames by 204 OFDM symbols.Set the insertion position of pilot signal as benchmark with this OFDM transmission frame unit.
Be used as in the ofdm system of modulating system of each subcarrier in the modulation of QAM system, because the influence of multichannel etc. between transmission period, amplitude is different with phase characteristic for each subcarrier signal.Therefore, at receiver side, need balanced received signal so that equal for the amplitude and the phase place of each subcarrier.In ofdm system,, in the transmission symbol of transmission signals, insert the pilot signal of predetermined amplitude and predetermined phase discretely in emitting side.At receiver side, use the amplitude of pilot signal and the frequency characteristic of phase calculation channel, and according to the balanced received signal of the characteristic of channel of calculating.
The pilot signal that is used for the calculating channel characteristic is known as scattered pilot (SP) signal.Figure 3 illustrates the configuration pattern in the OFDM symbol of the SP signal that in DVB-T standard and ISDB-T standard, adopts.
In OFDM receiver 10, carry out the appointment of this FFT the window's position by window regenerator 22.As window regenerator 22; for example, be used to utilize the OFDM time-domain signal to carry out the device of window regeneration according to the detection of the correlation of protection gap periods and be used to use delay section that postpones section estimator 21 estimation channels and the device of carrying out window regeneration.
Pilot tone is used channel estimator 17 to be extracted in the SP signal that inserts in the OFDM frequency-region signal that is calculated by FFT computing circuit 16 and is estimated the characteristic of channel of the subcarrier of configuration SP signal.
For example, use among the channel estimator 17A in pilot tone shown in Figure 4, the pilot tone in the OFDM receiver 10 uses channel estimator 17 to comprise SP signal extracting circuit 171, mean type time orientation channel estimator 172, interpolation type time orientation channel estimator 173, selector 174, Doppler frequency spectrum estimator 175 and maximum doppler frequency decision circuit 176.
Use among the channel estimator 17A in pilot tone, the OFDM frequency-region signal is offered SP signal extracting circuit 171 and Doppler frequency spectrum estimator 175.
SP signal extracting circuit 171 only is extracted in the SP signal that inserts in the position shown in Figure 3, and the modulation product of removal pilot signal is to calculate the characteristic of channel in the SP position.To offer mean type time orientation channel estimator 172 and interpolation type time orientation channel estimator 173 by the characteristic of channel in the SP position of SP signal extracting circuit 171 calculating.
Mean type time orientation channel estimator 172 comprises the elementary iir filter with structure shown in Fig. 5 A.Shown in Fig. 5 B, mean type time orientation channel estimator 172 will ask average by the channel estimation value in the SP position of SP signal extracting circuit 171 estimations.During SP signal adjacent on the time orientation, reuse IIR output.
Interpolation type time orientation channel estimator 173 comprises having the linear interpolation circuit of structure as shown in Figure 6A.Channel estimation value in the interpolation type time orientation channel estimator 173 SP position that interpolation is estimated by SP signal extracting circuit 171 on time orientation is to estimate channel during three symbols shown in Fig. 6 B.
Doppler frequency spectrum estimator 175 is the estimating Doppler frequency spectrum from the OFDM frequency-region signal.Maximum doppler frequency decision circuit 176 calculates maximum doppler frequency from the Doppler frequency spectrum of being estimated by Doppler frequency spectrum estimator 175.
The Doppler frequency spectrum that has fluctuateed in Fig. 7 A to Fig. 7 C, having illustrated corresponding to channel.When not fluctuation or fluctuation did not relax very much, shown in Fig. 7 A, frequency spectrum was to concentrate on 0[Hz] linear spectral.When fluctuation when being periodic, because can be by adding the approximate fluctuation of several sine waves, so can represent Doppler frequency spectrum by several line spectrums.The state of the Doppler frequency spectrum of being represented by two line spectrums has been shown in Fig. 7 B.When fluctuating at random, shown in Fig. 7 C, frequency spectrum launches and shows well-known vertical shaft type frequency spectrum.
Pilot tone in the OFDM receiver 10 is used channel estimator 17A Doppler frequency spectrum shown in calculating chart 7A to Fig. 7 C from the OFDM frequency-region signal, and from spectral shape and maximum doppler frequency, select the best approach of direction channel estimated time, to carry out estimation corresponding to the time orientation channel that fluctuates in the channel.
The output that selector 174 switches mean type time orientation channel estimator 172 and interpolation type time orientation channel estimator 173 according to the maximum doppler frequency from 176 outputs of maximum doppler frequency decision circuit.When maximum doppler frequency very hour, the mean type time orientation channel estimator 172 that selector 174 selects the mean type of time of implementation direction channels to estimate.When having fluctuation, the interpolation type time orientation channel estimator 173 that selector 174 selects the interpolation type of time of implementation direction channel to estimate.Therefore, the time fluctuation in the slow and channel of the time fluctuation in channel under two kinds of situations, can be carried out high performance channel estimating, and as shown in Figure 8, be that per three subcarriers of all OFDM symbols on frequency direction are estimated the characteristics of channel faster.
Channel distortion compensator 18 comprises compensator 181 and frequency direction channel estimator 182.
In channel distortion compensator 18, frequency direction channel estimator 182 make by pilot tone use channel estimator 17A be the characteristic of channel calculated of per three subcarriers on frequency direction through being subject to processing, to calculate the characteristic of channel of all subcarriers in the OFDM symbol as shown in Figure 9.As a result, can estimate the characteristic of channel for all subcarriers of OFDM symbol.Compensator 181 uses the characteristic of channel of all subcarriers that provided by frequency direction channel estimator 182 to remove distortion owing to channel from the OFDM frequency-region signal that is calculated by FFT computing circuit 16.
Transmission parameter decoder 20 extracts transmission parameter information by the subcarrier that inserts transmission parameter information is decoded from the OFDM frequency-region signal, and transmission parameter information is offered error correction circuit 19.
Error correction circuit 19 applies deinterleave according to the transmission parameter information that is provided by transmission parameter decoder 20 to OFDM frequency-region signal (therefrom removing channel distortion by channel distortion compensator 18) and handles.Error correction circuit 19 output OFDM frequency-region signals are as the decoded data by contraction decoding (depuncture), Viterbi, diffusion signal removal and RS decoding.
Postpone the impulse response of section estimator 21 calculating channels and impulse response is offered window regenerator 22.As postponing the section estimation approach; for example, adopt to use the method for matched filter (using the OFDM time-domain signal will protect gap periods to be set at tap coefficient) and by making the characteristic of channel that provides by pilot tone use channel estimator 17 stand the method that IFFT comes the computing relay section.
Use channel estimator 17 as pilot tone, the pilot tone that replaces switching mean type time orientation channel estimator 172 and interpolation type time orientation channel estimator 173 by selector 174 is used channel estimator 17A, can also adopt pilot tone use channel estimator 17B with structure shown in Figure 10 or the pilot tone with structure shown in Figure 12 to use channel estimator 17C.
Pilot tone shown in Figure 10 uses channel estimator 17B to comprise SP signal extracting circuit 171, interpolation type time orientation channel estimator 173, forecasting type time orientation channel estimator 177, selector 174, Doppler frequency spectrum estimator 175 and fluctuation type decision device 178.
Use among the channel estimator 17B in pilot tone, the OFDM frequency-region signal is offered SP signal extracting circuit 171 and Doppler frequency spectrum estimator 175.SP signal extracting circuit 171 only is extracted in the SP signal that inserts in the position shown in Figure 3 and the modulation product of removing pilot signal to calculate the characteristic of channel in the SP position.To offer interpolation type time orientation channel estimator 173 and forecasting type time orientation channel estimator 177 by the characteristic of channel in the SP position of SP signal extracting circuit 171 calculating.
Interpolation type time orientation channel estimator 173 comprises the variable coefficient FIR filter with structure shown in Fig. 6 A.Channel estimation value in the interpolation type time orientation channel estimator 173 SP position that interpolation is estimated by SP signal extracting circuit 171 on time orientation is to estimate channel during three symbols shown in Fig. 6 B.
Forecasting type time orientation channel estimator 177 comprises having for example elementary iir filter of structure shown in Figure 11 A.Shown in Figure 11 B, forecasting type time orientation channel estimator 177 will be by the channel estimation value in the SP position of SP signal extracting circuit 171 estimations as importing the channel of predicting in the next SP position.Up to the next SP signal of input, forecasting type time orientation channel estimator 177 interpolation prediction values are to generate estimated value.As the method for upgrading filter coefficient, the method for existence use lowest mean square (LMS) algorithm etc.
Doppler frequency spectrum estimator 175 is the estimating Doppler frequency spectrum from the OFDM frequency-region signal.Fluctuation type decision device 178 is judged the shape of the Doppler frequency spectrum of being estimated by Doppler frequency spectrum estimator 175.
The output that selector 174 switches mean type time orientation channel estimator 172 and forecasting type time orientation channel estimator 177 according to the judgement output of fluctuation type decision device 178.When the fluctuation in the channel is linear spectral, the forecasting type time orientation channel estimator 177 that selector 174 selects the forecasting type of time of implementation direction channel to estimate.When fluctuation is at random, that is, during spread spectrum, the interpolation type time orientation channel estimator 173 that selector 174 selects the interpolation type of time of implementation direction channels to estimate.Therefore, time fluctuation in channel is under periodic (comprising the situation that does not have fluctuation) and the channel fluctuation two kinds of situations at random, can carry out high performance channel estimating, and as shown in Figure 8, for per three subcarriers of all OFDM symbols on frequency direction are estimated the characteristic of channel.
Pilot tone shown in Figure 12 uses channel estimator 17C to comprise SP signal extracting circuit 171, mean type time orientation channel estimator 172, interpolation type time orientation channel estimator 173, forecasting type time orientation channel estimator 177, selector 174, Doppler frequency spectrum estimator 175, maximum doppler frequency decision circuit 176 and fluctuation type decision device 178.
Use channel estimator 17C by use the pilot tone shown in channel estimator 17A and Figure 10 to use channel estimator 17B to obtain pilot tone in conjunction with the pilot tone shown in Fig. 4.Use among the channel estimator 17C in pilot tone, Doppler frequency spectrum estimator 175 is the estimating Doppler frequency spectrum from the OFDM frequency-region signal.Maximum doppler frequency decision circuit 176 calculates maximum doppler frequency.When this maximum doppler frequency hour, select the mean type method of direction channel estimated time.When fluctuation was big, fluctuation type decision device 178 judged that fluctuation is cyclic fluctuation or random fluctuation.When fluctuation is cyclic fluctuation, select the forecasting type method of direction channel estimated time.When fluctuation is random fluctuation, select the interpolation type method of direction channel estimated time.This makes and can or not exist and method of estimation that the type selecting that fluctuates is suitable and carry out high performance channel estimating according to the existence of fluctuating in the channel.
For example, as shown in figure 13, fluctuation type decision device 178 comprises center reduction (center clip) circuit 1781, positive maximum Doppler searcher 1782, negative maximum Doppler searcher 1783, interval 0 counting circuit 1784 of fd and decision maker 1785.
In fluctuation type decision device 178, at first, in order to remove noise component(s), the center is cut down 1781 pairs of frequency spectrums of circuit and is applied center reduction processing.The center is cut down circuit 1781 and deduct threshold value from frequency spectrum, and forces to substitute negative part with 0 and cut down processing with implementation center.To cut down the frequency spectrum of handling through acceptor center and offer positive maximum Doppler searcher 1782, negative maximum Doppler searcher 1783 and interval 0 counting circuit 1784 of fd.The maximum positive exponent (index) of positive maximum Doppler searcher 1782 search nonzero values.The negative maximal index of negative maximum Doppler searcher 1783 search nonzero values.0 index between the negative maximum Doppler index of the fd positive maximum Doppler exponential sum of interval 0 counting circuit 1784 countings.
Decision maker 1785 is judged spectral shape according to the process shown in the flow chart among Figure 14.
At first, decision maker 1785 deducts negative maximal index from positive maximal index, to calculate Doppler's expansion (hereinafter being called " Fds ") (step S1).
Decision maker 1785 judges that whether Doppler's expansion (Fds) of calculating is less than threshold value (step S2) in step S1.
Result of determination in step S2 is a true time, that is, Fds is less than threshold value, and decision maker 1785 judges that channel is the channel (step S4) that does not have fluctuation, and finishes to be used to judge the processing of spectral shape.
Shown in Figure 15 A to Figure 15 C when not fluctuating the decision state of the shape of Doppler frequency spectrum.
Shown in Figure 15 A, the center is cut down 1781 pairs of Doppler frequency spectrums that calculated by Doppler frequency spectrum estimator 175 of circuit and is applied the center and cut down and handle, with obtain shown in Figure 15 B from wherein having removed the Doppler frequency spectrum of noise.Shown in Figure 15 C, when the Doppler of Doppler frequency spectrum expanded (Fds) less than threshold value, decision maker 1785 judged that channels are the channels that do not have fluctuation.
When the result of determination in step S2 is a fictitious time, that is, Fds is equal to or greater than threshold value, and decision maker 1785 judges that fluctuation is cyclic fluctuation or random fluctuation (step S3).
Can be based on the determination processing among the ratio execution in step S3 in 0 interval in Doppler's expansion.When 0 the number (hereinafter being called nzero) that provides by interval 0 counting circuit 1784 of fd greater than Fds *During scaling (scaling) (that is, 0.9) (step S3: true), decision maker 1785 thinks that fluctuation is cyclic fluctuation (step S5).Number when 0 is not more than Fds *(step S3: vacation), decision maker 1785 thinks that fluctuation is random fluctuation (step S6), and finishes to be used to judge the processing of spectral shape during scaling.
Be the decision state that is the shape of Doppler frequency spectrum periodically the time shown in Figure 16 A to Figure 16 C when fluctuating.
Shown in Figure 16 A, the center is cut down 1781 pairs of Doppler frequency spectrums that calculated by Doppler frequency spectrum estimator 175 of circuit and is applied the center and cut down and handle, with obtain shown in Figure 16 B from wherein having removed the Doppler frequency spectrum of noise.Shown in Figure 16 C, the number of 0 index between the negative maximum Doppler index of positive maximum Doppler exponential sum is greater than Fds *During scaling, decision maker 1785 judges that channel is the channel of cyclic fluctuation.
Be the decision state that is the shape of Doppler frequency spectrum at random the time shown in Figure 17 A to Figure 17 C when fluctuating.
Shown in Figure 17 A, the center is cut down 1781 pairs of Doppler frequency spectrums that calculated by Doppler frequency spectrum estimator 175 of circuit and is applied the center and cut down and handle, with obtain shown in Figure 17 B from wherein having removed the Doppler frequency spectrum of noise.Shown in Figure 16 C, the number of 0 index between the negative maximum Doppler index of positive maximum Doppler exponential sum is equal to or less than Fds *During scaling, decision maker 1785 judges that channel is the channel of random fluctuation.
In OFDM receiver 10 according to this embodiment, according to the output of fluctuation type decision device 178, selector 174 is selected mean type time orientation channel estimator 172, is being selected forecasting type time orientation channel estimator 177 under the situation of periodicity time fluctuation and select interpolation type time orientation channel estimator 173 under the situation of randomness time fluctuation when channel is static state.
As above describe, selector 174 is according in output selectivity ground switching mean type time orientation channel estimator 172, forecasting type time orientation channel estimator 177 and the interpolation type time orientation channel estimator 173 of fluctuation type decision device 178 any one.Therefore, can select suitable method of estimation according to channel status, and not increase circuit scale, and in all channels, obtain remarkable receptivity.
It should be appreciated by those skilled in the art, multiple modification, combination, recombinant and improvement to be arranged, all should be included within the scope of claim of the present invention or equivalent according to designing requirement and other factors.

Claims (9)

1. OFDM receiver comprises:
The ofdm signal receiving system is used to receive OFDM (OFDM) signal;
The channel characteristic estimation device is used for using the pilot signal of the described ofdm signal that is received by described ofdm signal receiving system to estimate the characteristic of channel; And
The transmission distortion compensation arrangement is used for based on the described characteristic of channel by described channel characteristic estimation device estimation the described ofdm signal that is received by described ofdm signal receiving system being applied the processing that is used to compensate transmission distortion, wherein,
Described channel characteristic estimation device comprises:
Polytype time orientation channel estimating apparatus is used to estimate the characteristic of channel; And
Switching control is used for switching these estimation units according to channel status.
2. OFDM receiver according to claim 1, wherein, described switching control comprises the Doppler frequency spectrum estimation unit, be used to the described ofdm signal estimating Doppler frequency spectrum that is received by described ofdm signal receiving system, described switching control switches the described polytype time orientation channel estimating apparatus that is used to estimate the characteristic of channel according to the described Doppler frequency spectrum of being estimated by described Doppler frequency spectrum estimation unit.
3. OFDM receiver according to claim 2, wherein, described switching control comprises the maximum doppler frequency decision maker, be used for calculating maximum doppler frequency, and switch described polytype time orientation channel estimating apparatus according to described maximum doppler frequency according to the described Doppler frequency spectrum of estimating by described Doppler frequency spectrum estimation unit.
4. OFDM receiver according to claim 2, wherein, described switching control comprises fluctuation type decision device, be used to judge the shape of the described Doppler frequency spectrum of estimating by described Doppler frequency spectrum estimation unit, and switch described polytype time orientation channel estimating apparatus according to the shape of described Doppler frequency spectrum.
5. OFDM receiver according to claim 4, wherein, described fluctuation type decision device is cyclic fluctuation or random fluctuation according to the shape decision channel fluctuation of the described Doppler frequency spectrum of being estimated by described Doppler frequency spectrum estimation unit.
6. OFDM receiver according to claim 5, wherein, described fluctuation type decision device comprises:
The center cutting device is used for that the described Doppler frequency spectrum of being estimated by described Doppler frequency spectrum estimation unit is applied the center and cuts down processing;
Positive maximum Doppler searcher is used to by described center cutting device and has applied the maximum positive exponent that the described Doppler frequency spectrum search nonzero value of handling is cut down at described center;
Bear the maximum Doppler searcher, be used to search for the negative maximal index of nonzero value;
Counting device is used to have applied described center by described center cutting device and cut down the counting that the described Doppler frequency spectrum of handling carries out the index of 0 value between the described negative maximum Doppler index that the described positive maximum Doppler exponential sum that detected by described positive maximum Doppler searcher detects by described negative maximum Doppler searcher;
Decision maker, be used for deducting the described negative maximum Doppler index that detects by described negative maximum Doppler searcher from the described positive maximum Doppler index that detects by described positive maximum Doppler searcher, to calculate Doppler's expansion, when the Doppler who calculates expands less than threshold value, judge that channel is the channel that does not have fluctuation, when described Doppler's expansion is equal to or greater than described threshold value, 0 value interval in described Doppler expansion judges that described channel fluctuation is cyclic fluctuation during greater than threshold value, and judges that described channel fluctuation is random fluctuation when being not more than described threshold value in described interval.
7. OFDM receiver according to claim 2, wherein, described switching control comprises:
The maximum doppler frequency decision maker is used for calculating maximum doppler frequency according to the described Doppler frequency spectrum of being estimated by described Doppler frequency spectrum estimation unit, and switches described polytype time orientation channel estimating apparatus according to described maximum doppler frequency; And
Fluctuation type decision device is used to judge the shape by the described Doppler frequency spectrum of described Doppler frequency spectrum estimation unit estimation, and switches described polytype time orientation channel estimating apparatus according to the shape of described Doppler frequency spectrum.
8. ofdm signal method of reseptance, receive OFDM (OFDM) signal, use the pilot signal in the ofdm signal that is received to estimate the characteristic of channel, and the ofdm signal that is received is applied the processing that is used to compensate transmission distortion based on the estimated characteristic of channel, described ofdm signal method of reseptance may further comprise the steps:
Be the ofdm signal estimating Doppler frequency spectrum that is received; And
According to the Doppler frequency spectrum of estimating, switch the polytype time orientation channel estimating apparatus that is used to estimate the characteristic of channel.
9. OFDM receiver comprises:
The ofdm signal receiving element receives OFDM (OFDM) signal;
The channel characteristic estimation unit is used for using the pilot signal of the described ofdm signal that is received by described ofdm signal receiving element to estimate the characteristic of channel; And
The transmission distortion compensating unit is used for based on the described characteristic of channel by described channel characteristic estimation unit estimation, and the described ofdm signal that is received by described ofdm signal receiving element is applied the processing that is used to compensate transmission distortion, wherein,
Described channel characteristic estimation unit comprises:
Polytype time orientation channel estimating unit is used to estimate the characteristic of channel; And
Switch control unit is used for switching these estimation units according to channel status.
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